By default, plain objects are not iterable. But you can make the object iterable by defining a Symbol.iterator property on it.
Let’s demonstrate this with an example:
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 | const collection = { one: 1, two: 2, three: 3, [Symbol.iterator]() { const values = Object.keys(this); let i = 0; return { next: () => { return { value: this[values[i++]], done: i > values.length } } }; } }; const iterator = collection[Symbol.iterator](); console.log(iterator.next()); // → {value: 1, done: false} console.log(iterator.next()); // → {value: 2, done: false} console.log(iterator.next()); // → {value: 3, done: false} console.log(iterator.next()); // → {value: undefined, done: true} |
The above process can be simplified using a generator function,
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 | const collection = { one: 1, two: 2, three: 3, [Symbol.iterator]: function * () { for (let key in this) { yield this[key]; } } }; const iterator = collection[Symbol.iterator](); console.log(iterator.next()); // {value: 1, done: false} console.log(iterator.next()); // {value: 2, done: false} console.log(iterator.next()); // {value: 3, done: false} console.log(iterator.next()); // {value: undefined, done: true} |
If you like this question & answer and want to contribute, then write your question & answer and email to freewebmentor[@]gmail.com. Your question and answer will appear on FreeWebMentor.com and help other developers.
